1. Field of the Invention
The present invention relates to a hydraulic tensioner lifter which applies tension to an endless transmission belt such as a chain or belt used in the transmission mechanism of an internal combustion engine.
2. Description of Background Art
Conventionally, in an internal combustion engine, a hydraulic tensioner lifter has been used in order to apply tension to an endless transmission belt used in the transmission mechanism, such as a chain. This hydraulic tensioner lifter uses a method which pushes a plunger by means of tensioner spring and oil pressure, where as the plunger stretches, a stretched lifter gives the chain a prescribed tension to suppress oscillation of the chain and ensure stable chain drive. See, for example, JP-A No. 287092/2003 Pages 6-7 and FIG. 2.
The hydraulic tensioner lifter as described in JP-A No. 287092/2003 includes a tensioner lifter body, a hole made in the lifter body, a plunger which is slidably fitted in the hole for forming an oil chamber in the hole of the lifter body and a tensioner spring which biases the plunger in a way to push it out of the hole, where the tensioner spring is located between the bottom of the hole and a plunger adjacent to the oil chamber side end face of an orifice member and as the plunger is pushed out by this tensioner spring and oil pressure fed into the oil chamber, it applies tension to the chain of the internal combustion engine.
In the above hydraulic tensioner lifter, while the internal combustion engine is not working, the hydraulic pump also stops working and the oil in the oil circuit of the hydraulic tensioner lifter falls down by the pull of gravity, causing air to enter the oil circuit of the hydraulic tensioner lifter. Therefore, when the engine is started, it takes some time to remove the air from the oil circuit of the hydraulic tensioner lifter and fill the oil circuit with oil.
Before the oil circuit of the hydraulic tensioner lifter is filled with oil, the endless transmission belt turns with the operation of the internal combustion engine and thus a pushing force is irregularly applied to the plunger of the hydraulic tensioner lifter. Consequently, the plunger is deeply pushed inward by a large pushing force and the plunger base end touches the tensioner body. Also, at the time of start, noise may be generated during transition of the chain from a loose state to a tense state.
If the spring constant of the tensioner spring is increased in order to avoid this, the spring force of the tensioner spring would rapidly grow with an increase in the plunging amount of the plunger, which would cause an excessive force to be applied to the endless transmission belt and thus resulting in an excessive tension on the endless transmission belt.